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Subject: Re: [PATCH v4 1/2] NFSD: delay unmount source's export after
 inter-server copy completed.
To:     "J. Bruce Fields" <bfields@fieldses.org>,
        Olga Kornievskaia <olga.kornievskaia@gmail.com>
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        linux-nfs <linux-nfs@vger.kernel.org>
References: <20210423205946.24407-1-dai.ngo@oracle.com>
 <20210423205946.24407-2-dai.ngo@oracle.com>
 <CAN-5tyGS9z1+So-MAiWEX-a6-qCGxzm_mW82dt4DTV2E-SBKtg@mail.gmail.com>
 <20210514184235.GA16955@fieldses.org>
From:   dai.ngo@oracle.com
Message-ID: <6b6cb87d-75fd-cc0d-5642-d8e65a897ed7@oracle.com>
Date:   Fri, 14 May 2021 13:19:40 -0700
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On 5/14/21 11:42 AM, J. Bruce Fields wrote:
> On Fri, May 14, 2021 at 02:12:38PM -0400, Olga Kornievskaia wrote:
>> On Fri, Apr 23, 2021 at 4:59 PM Dai Ngo <dai.ngo@oracle.com> wrote:
>>> Currently the source's export is mounted and unmounted on every
>>> inter-server copy operation. This patch is an enhancement to delay
>>> the unmount of the source export for a certain period of time to
>>> eliminate the mount and unmount overhead on subsequent copy operations.
>>>
>>> After a copy operation completes, a delayed task is scheduled to
>>> unmount the export after a configurable idle time. Each time the
>>> export is being used again, its expire time is extended to allow
>>> the export to remain mounted.
>>>
>>> The unmount task and the mount operation of the copy request are
>>> synced to make sure the export is not unmounted while it's being
>>> used.
>>>
>>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>>> ---
>>>   fs/nfsd/nfs4proc.c      | 178 ++++++++++++++++++++++++++++++++++++++++++++++--
>>>   fs/nfsd/nfsd.h          |   4 ++
>>>   fs/nfsd/nfssvc.c        |   3 +
>>>   include/linux/nfs_ssc.h |  20 ++++++
>>>   4 files changed, 201 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
>>> index dd9f38d072dd..a4b110cbcab5 100644
>>> --- a/fs/nfsd/nfs4proc.c
>>> +++ b/fs/nfsd/nfs4proc.c
>>> @@ -55,6 +55,81 @@ module_param(inter_copy_offload_enable, bool, 0644);
>>>   MODULE_PARM_DESC(inter_copy_offload_enable,
>>>                   "Enable inter server to server copy offload. Default: false");
>>>
>>> +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
>>> +static int nfsd4_ssc_umount_timeout = 900000;          /* default to 15 mins */
>>> +module_param(nfsd4_ssc_umount_timeout, int, 0644);
>>> +MODULE_PARM_DESC(nfsd4_ssc_umount_timeout,
>>> +               "idle msecs before unmount export from source server");
>>> +
>>> +static void nfsd4_ssc_expire_umount(struct work_struct *work);
>>> +static struct nfsd4_ssc_umount nfsd4_ssc_umount;
>>> +
>>> +/* nfsd4_ssc_umount.nsu_lock must be held */
>>> +static void nfsd4_scc_update_umnt_timo(void)
>>> +{
>>> +       struct nfsd4_ssc_umount_item *ni = 0;
>>> +
>>> +       cancel_delayed_work(&nfsd4_ssc_umount.nsu_umount_work);
>>> +       if (!list_empty(&nfsd4_ssc_umount.nsu_list)) {
>>> +               ni = list_first_entry(&nfsd4_ssc_umount.nsu_list,
>>> +                       struct nfsd4_ssc_umount_item, nsui_list);
>>> +               nfsd4_ssc_umount.nsu_expire = ni->nsui_expire;
>>> +               schedule_delayed_work(&nfsd4_ssc_umount.nsu_umount_work,
>>> +                       ni->nsui_expire - jiffies);
>>> +       } else
>>> +               nfsd4_ssc_umount.nsu_expire = 0;
>>> +}
>>> +
>>> +static void nfsd4_ssc_expire_umount(struct work_struct *work)
>>> +{
>>> +       bool do_wakeup = false;
>>> +       struct nfsd4_ssc_umount_item *ni = 0;
>>> +       struct nfsd4_ssc_umount_item *tmp;
>>> +
>>> +       spin_lock(&nfsd4_ssc_umount.nsu_lock);
>>> +       list_for_each_entry_safe(ni, tmp, &nfsd4_ssc_umount.nsu_list, nsui_list) {
>>> +               if (time_after(jiffies, ni->nsui_expire)) {
>>> +                       if (refcount_read(&ni->nsui_refcnt) > 0)
>>> +                               continue;
>>> +
>>> +                       /* mark being unmount */
>>> +                       ni->nsui_busy = true;
>>> +                       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +                       mntput(ni->nsui_vfsmount);
>>> +                       spin_lock(&nfsd4_ssc_umount.nsu_lock);
>>> +
>>> +                       /* waiters need to start from begin of list */
>>> +                       list_del(&ni->nsui_list);
>>> +                       kfree(ni);
>>> +
>>> +                       /* wakeup ssc_connect waiters */
>>> +                       do_wakeup = true;
>>> +                       continue;
>>> +               }
>>> +               break;
>> Wouldn't you be exiting your iteration loop as soon as you find a
>> delayed item that hasn't expired? What if other items on the list have
>> expired?
>>
>> It looks like the general design is that work for doing umount is
>> triggered by doing some copy, right? And then it just keeps
>> rescheduling itself? Shouldn't we just be using the laundrymat instead
>> that wakes up and goes thru the list mounts that are put to be
>> unmounted and does so? Bruce previously had suggested using laundrymat
>> for cleaning up copynotify states on the source server. But if the
>> existing approach works for Bruce, I'm ok with it too.
> I guess I'd prefer to use the laundromat, unless there's some reason to
> do this one differently.

I will look into the laundromat approach.  I try to avoid destabilizing
existing code by using separate mechanism for SSC.

>
> Also: on a quick skim, I don't see where this is shut down?  (If the
> server is shut down, or the module unloaded?)

Ah thanks! I completely miss this part. I will add this in v5 patch.

-Dai

>
> --b.
>
>>> +       }
>>> +       nfsd4_scc_update_umnt_timo();
>>> +       if (do_wakeup)
>>> +               wake_up_all(&nfsd4_ssc_umount.nsu_waitq);
>>> +       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +}
>>> +
>>> +static DECLARE_DELAYED_WORK(nfsd4, nfsd4_ssc_expire_umount);
>>> +
>>> +void nfsd4_ssc_init_umount_work(void)
>>> +{
>>> +       if (nfsd4_ssc_umount.nsu_inited)
>>> +               return;
>>> +       INIT_DELAYED_WORK(&nfsd4_ssc_umount.nsu_umount_work,
>>> +               nfsd4_ssc_expire_umount);
>>> +       INIT_LIST_HEAD(&nfsd4_ssc_umount.nsu_list);
>>> +       spin_lock_init(&nfsd4_ssc_umount.nsu_lock);
>>> +       init_waitqueue_head(&nfsd4_ssc_umount.nsu_waitq);
>>> +       nfsd4_ssc_umount.nsu_inited = true;
>>> +}
>>> +EXPORT_SYMBOL_GPL(nfsd4_ssc_init_umount_work);
>>> +#endif
>>> +
>>>   #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
>>>   #include <linux/security.h>
>>>
>>> @@ -1181,6 +1256,9 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
>>>          char *ipaddr, *dev_name, *raw_data;
>>>          int len, raw_len;
>>>          __be32 status = nfserr_inval;
>>> +       struct nfsd4_ssc_umount_item *ni = 0;
>>> +       struct nfsd4_ssc_umount_item *work, *tmp;
>>> +       DEFINE_WAIT(wait);
>>>
>>>          naddr = &nss->u.nl4_addr;
>>>          tmp_addrlen = rpc_uaddr2sockaddr(SVC_NET(rqstp), naddr->addr,
>>> @@ -1229,12 +1307,68 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
>>>                  goto out_free_rawdata;
>>>          snprintf(dev_name, len + 5, "%s%s%s:/", startsep, ipaddr, endsep);
>>>
>>> +       work = kzalloc(sizeof(*work), GFP_KERNEL);
>>> +try_again:
>>> +       spin_lock(&nfsd4_ssc_umount.nsu_lock);
>>> +       list_for_each_entry_safe(ni, tmp, &nfsd4_ssc_umount.nsu_list, nsui_list) {
>>> +               if (strncmp(ni->nsui_ipaddr, ipaddr, sizeof(ni->nsui_ipaddr)))
>>> +                       continue;
>>> +               /* found a match */
>>> +               if (ni->nsui_busy) {
>>> +                       /*  wait - and try again */
>>> +                       prepare_to_wait(&nfsd4_ssc_umount.nsu_waitq, &wait,
>>> +                               TASK_INTERRUPTIBLE);
>>> +                       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +
>>> +                       /* allow 20secs for mount/unmount for now - revisit */
>>> +                       if (signal_pending(current) ||
>>> +                                       (schedule_timeout(20*HZ) == 0)) {
>>> +                               status = nfserr_eagain;
>>> +                               kfree(work);
>>> +                               goto out_free_devname;
>>> +                       }
>>> +                       finish_wait(&nfsd4_ssc_umount.nsu_waitq, &wait);
>>> +                       goto try_again;
>>> +               }
>>> +               ss_mnt = ni->nsui_vfsmount;
>>> +               if (refcount_read(&ni->nsui_refcnt) == 0)
>>> +                       refcount_set(&ni->nsui_refcnt, 1);
>>> +               else
>>> +                       refcount_inc(&ni->nsui_refcnt);
>>> +               spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +               kfree(work);
>>> +               goto out_done;
>>> +       }
>>> +       /* create new entry, set busy, insert list, clear busy after mount */
>>> +       if (work) {
>>> +               strncpy(work->nsui_ipaddr, ipaddr, sizeof(work->nsui_ipaddr));
>>> +               refcount_set(&work->nsui_refcnt, 1);
>>> +               work->nsui_busy = true;
>>> +               list_add_tail(&work->nsui_list, &nfsd4_ssc_umount.nsu_list);
>>> +       }
>>> +       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +
>>>          /* Use an 'internal' mount: SB_KERNMOUNT -> MNT_INTERNAL */
>>>          ss_mnt = vfs_kern_mount(type, SB_KERNMOUNT, dev_name, raw_data);
>>>          module_put(type->owner);
>>> -       if (IS_ERR(ss_mnt))
>>> +       if (IS_ERR(ss_mnt)) {
>>> +               if (work) {
>>> +                       spin_lock(&nfsd4_ssc_umount.nsu_lock);
>>> +                       list_del(&work->nsui_list);
>>> +                       wake_up_all(&nfsd4_ssc_umount.nsu_waitq);
>>> +                       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +                       kfree(work);
>>> +               }
>>>                  goto out_free_devname;
>>> -
>>> +       }
>>> +       if (work) {
>>> +               spin_lock(&nfsd4_ssc_umount.nsu_lock);
>>> +               work->nsui_vfsmount = ss_mnt;
>>> +               work->nsui_busy = false;
>>> +               wake_up_all(&nfsd4_ssc_umount.nsu_waitq);
>>> +               spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +       }
>>> +out_done:
>>>          status = 0;
>>>          *mount = ss_mnt;
>>>
>>> @@ -1301,10 +1435,46 @@ static void
>>>   nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct nfsd_file *src,
>>>                          struct nfsd_file *dst)
>>>   {
>>> +       bool found = false;
>>> +       bool resched = false;
>>> +       long timeout;
>>> +       struct nfsd4_ssc_umount_item *tmp;
>>> +       struct nfsd4_ssc_umount_item *ni = 0;
>>> +
>>>          nfs42_ssc_close(src->nf_file);
>>> -       fput(src->nf_file);
>>>          nfsd_file_put(dst);
>>> -       mntput(ss_mnt);
>>> +       fput(src->nf_file);
>>> +
>>> +       timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
>>> +       spin_lock(&nfsd4_ssc_umount.nsu_lock);
>>> +       list_for_each_entry_safe(ni, tmp, &nfsd4_ssc_umount.nsu_list,
>>> +               nsui_list) {
>>> +               if (ni->nsui_vfsmount->mnt_sb == ss_mnt->mnt_sb) {
>>> +                       list_del(&ni->nsui_list);
>>> +                       /*
>>> +                        * vfsmount can be shared by multiple exports,
>>> +                        * decrement refcnt and schedule delayed task
>>> +                        * if it drops to 0.
>>> +                        */
>>> +                       if (refcount_dec_and_test(&ni->nsui_refcnt))
>>> +                               resched = true;
>>> +                       ni->nsui_expire = jiffies + timeout;
>>> +                       list_add_tail(&ni->nsui_list, &nfsd4_ssc_umount.nsu_list);
>>> +                       found = true;
>>> +                       break;
>>> +               }
>>> +       }
>>> +       if (!found) {
>>> +               spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>> +               mntput(ss_mnt);
>>> +               return;
>>> +       }
>>> +       if (resched && !nfsd4_ssc_umount.nsu_expire) {
>>> +               nfsd4_ssc_umount.nsu_expire = ni->nsui_expire;
>>> +               schedule_delayed_work(&nfsd4_ssc_umount.nsu_umount_work,
>>> +                               timeout);
>>> +       }
>>> +       spin_unlock(&nfsd4_ssc_umount.nsu_lock);
>>>   }
>>>
>>>   #else /* CONFIG_NFSD_V4_2_INTER_SSC */
>>> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
>>> index 8bdc37aa2c2e..b3bf8a5f4472 100644
>>> --- a/fs/nfsd/nfsd.h
>>> +++ b/fs/nfsd/nfsd.h
>>> @@ -483,6 +483,10 @@ static inline bool nfsd_attrs_supported(u32 minorversion, const u32 *bmval)
>>>   extern int nfsd4_is_junction(struct dentry *dentry);
>>>   extern int register_cld_notifier(void);
>>>   extern void unregister_cld_notifier(void);
>>> +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
>>> +extern void nfsd4_ssc_init_umount_work(void);
>>> +#endif
>>> +
>>>   #else /* CONFIG_NFSD_V4 */
>>>   static inline int nfsd4_is_junction(struct dentry *dentry)
>>>   {
>>> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
>>> index 6de406322106..2558db55b88b 100644
>>> --- a/fs/nfsd/nfssvc.c
>>> +++ b/fs/nfsd/nfssvc.c
>>> @@ -322,6 +322,9 @@ static int nfsd_startup_generic(int nrservs)
>>>          ret = nfs4_state_start();
>>>          if (ret)
>>>                  goto out_file_cache;
>>> +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
>>> +       nfsd4_ssc_init_umount_work();
>>> +#endif
>>>          return 0;
>>>
>>>   out_file_cache:
>>> diff --git a/include/linux/nfs_ssc.h b/include/linux/nfs_ssc.h
>>> index f5ba0fbff72f..1e07be2a89fa 100644
>>> --- a/include/linux/nfs_ssc.h
>>> +++ b/include/linux/nfs_ssc.h
>>> @@ -8,6 +8,7 @@
>>>    */
>>>
>>>   #include <linux/nfs_fs.h>
>>> +#include <linux/sunrpc/svc.h>
>>>
>>>   extern struct nfs_ssc_client_ops_tbl nfs_ssc_client_tbl;
>>>
>>> @@ -52,6 +53,25 @@ static inline void nfs42_ssc_close(struct file *filep)
>>>          if (nfs_ssc_client_tbl.ssc_nfs4_ops)
>>>                  (*nfs_ssc_client_tbl.ssc_nfs4_ops->sco_close)(filep);
>>>   }
>>> +
>>> +struct nfsd4_ssc_umount_item {
>>> +       struct list_head nsui_list;
>>> +       bool nsui_busy;
>>> +       refcount_t nsui_refcnt;
>>> +       unsigned long nsui_expire;
>>> +       struct vfsmount *nsui_vfsmount;
>>> +       char nsui_ipaddr[RPC_MAX_ADDRBUFLEN];
>>> +};
>>> +
>>> +struct nfsd4_ssc_umount {
>>> +       struct list_head nsu_list;
>>> +       struct delayed_work nsu_umount_work;
>>> +       spinlock_t nsu_lock;
>>> +       unsigned long nsu_expire;
>>> +       wait_queue_head_t nsu_waitq;
>>> +       bool nsu_inited;
>>> +};
>>> +
>>>   #endif
>>>
>>>   /*
>>> --
>>> 2.9.5
>>>